Modern Phys Unit 1

Alpha Decay Equation

Parent nucleus → Daughter Nucleus + Helium-4

What happens to the daughter nucleus in alpha decay?

Loses 4 nucleons and 2 protons to form the alpha particle

Beta-Minus decay equation

Parent nucleus → electron + daughter + antineutrino

What happens to the daughter nucleus in beta-minus decay?

Gains a proton

Beta-plus decay equation

parent nucleus → positron + daughter nucleus + neutrino

What happens to the daughter nucleus in beta-plus decay?

Loses a proton

Annihilation

A subatomic particle collides with its matching antiparticle, causing both to disappear and convert their mass into pure energy

Neutrino

Tiny subatomic particle that has no electric charge and a very small mass.

What happens if Q > 0

Decay can occur

Mass of electron

0.0005 u

What is special about the KE of the recoiling nucleus in beta decay?

It’s very small because its mass is much larger than the electron/positron mass

Beta particle energy spectrum

Beta particle can have any KE value from 0 up to a maximum value because the energy is shared with the neutrino and the recoiling nucleus.

What does the peak in the beta particle energy spectrum signify?

the kinetic energy at which the greatest number of beta particles are emitted (the most probable energy).

Gamma Decay Equation

Excited nucleus * → nucleus + gamma ray

What happens if a nucleus is in an excited state?

It will release a photon (most commonly happens after alpha or beta decay)

Meta-Stable

a nucleus is in an excited state that lasts significantly longer than a typical excited nuclear state before releasing its excess energy

Half Life Equation

N = N0 (1/2)^n

Half Life Equation With Lambda

N = N0e^-lambda(t)

What does a larger lambda signify?

More decay, more activity

What is lambda

Lambda = 0.693/T_1/2

How is decays/s written as

s^-1

Shorter Half Life exposure

Activity is higher which causes more biological damage in a given amount of time

Longer half Life exposure

Lower activity but we have to worry about it for longer

What is the relationship between KE and mass in alpha decay?

ratios of KE is inversely proportional to ratio of masses (Kalpha/Kdaughter = massdaughter/massalpha)

How does the KE of a particle emitted from alpha decay compare to the KE of daughter nucleus

KE of alpha particle > KE of daughter nucleus

What happens to the momentum in alpha decay before and after?

Theyre the same, so 0

What happens to the mass of products vs parent in alpha decay?

Mass of products is < than mass of parent

What happens if there’s a high Eb/A

The nucleus is more stable, mass of nucleus must be less than that of its constitutent nucleons so that energy input is needed to break it apart